At least one cleaning machine of the above type is known and available on the market. It serves the purpose of opening the fibres conveyed in the delivery air and removing the impurities therein. The fibre material is pulled over the bar grates, whereby impurities penetrate through the bar grates and are then sucked up.
At present, it is known that bale opening machines, for example, those sold by the assignee of the present invention on a world wide basis under the name of UNIFLOC, deliver a relatively even flock stream to the following delivery air stream which, however, can again result in small accumulations of fibre flocks in the course of the pneumatic transport. The fibre flocks should be reopened by the cleaning machine according to the invention before the flocks delivered by the bale opening machine can be processed.